1. Field of the Invention
Aspects of the present invention relate to a negative electrode active material, a negative electrode having the same, and a lithium secondary battery including the negative electrode.
2. Description of the Related Art
While lithium metals are commonly used as negative electrode active materials, these metals can cause a short circuit in a battery, due to the formation of dendrites, resulting in a risk of explosion. For this reason, carbonaceous materials have recently been used in place of lithium metals, as negative electrode active materials.
Carbonaceous negative electrode active materials for a lithium battery include crystalline carbons, such as natural graphite and artificial graphite, and amorphous carbons, such as soft carbon and hard carbon. Amorphous carbon has a high capacity, but is highly irreversible in a charge/discharge cycle. Crystalline carbon, e.g., graphite, has a sufficiently high theoretical capacity (372 mAh/g) to be used as a negative electrode active material, but is rapidly degraded, resulting in a short lifespan. Also, a carbonaceous active material cannot be use in a negative electrode of a high capacity lithium battery, since its theoretical capacity does not exceed 372 mAh/g.
In an effort to overcome these problems, metal-graphite composite negative electrode active materials, including graphite and, for example, aluminum (Al), germanium (Ge), silicon (Si), tin (Sn), zinc (Zn) and/or lead (Pb), are being actively studied for use in lithium batteries. However, in such composite negative electrode active materials, lithium ions may be intercalated into inorganic particles, such as Si or Sn, included in the composite negative electrode active material, during charging, and thus, the inorganic particles may expand by about 300 to 400%.
Further, when lithium ions are deintercalated during discharging, the inorganic particles contract. As the charge/discharge cycles are repeated, the conductivity of such active materials may be decreased, due to the volume changes of the inorganic particles. In addition, such a negative electrode active material may separate from a negative electrode collector, resulting in a drastic decrease in cycle-life.